ABSTRACT
The purpose of performing antimicrobial susceptibility testing is to provide in vitro data to help ensure that appropriate and adequate antimicrobial therapy is used to optimize treatment outcomes. Etest is a gradient technique that combines the principles of both the disk diffusion and agar dilution methods. Modifications for broth microdilution can also be used for testing fastidious organisms, although panels must be read manually and not by automated instruments. Shortly afterward, a broth microdilution method for rapidly growing anaerobes was included in the reference standard; however, the method is only described for a limited number of antimicrobials and the panels are not commercially available. The CLSI reference methods for fungi include disk diffusion, as well as broth macro and microdilution. Susceptibility testing of rapidly growing mycobacteria can be performed by either broth microdilution or by Etest. In some instances, the antibiotic susceptibility testing will result in a different phenotypic pattern than what is predicted with molecular testing.
